This invention relates to an electromagnetic pump of the type for feeding fuel to an internal combustion engine of a motor car, for example.
The electromagnetic pump of this type is required to have a simple construction, the capability of being machined and assembled accurately with low labor content and the capability of stable operation. Prior art electromagnetic pumps can not fulfill all of these requirements.
For example, an electromagnetic pump disclosed in U.S. Pat. No. 3,400,663 comprises a nonmagnetic sleeve containing a plunger, an inlet fixture and an outlet fixture secured to the opposite ends of the plunger, and a U shaped yoke acting as a frame, the opposing legs of the yoke being provided with aligned openings for mounting the inlet and outlet fixtures respectively in a coaxial relationship. The yoke is prepared by bending a relatively thick magnetic plate of iron or steel and functions to form a flux path for reciprocating the plunger when an exciting coil wound about the sleeve is energized. After assembly with various components parts, the yoke is fitted into a housing constructed to close the opening of the yoke, thus forming a portion of a container for the electromagnetic pump.
In such prior art electromagnetic pump, since the yoke is formed by bending a relatively thick plate, not only is the bending operation troublesome but also there is a fear that the bent legs will not extend exactly in the horizontal direction, or the legs may deflect, thus making it impossible to form parallel legs. With such a deformed yoke, it is difficult to coaxially arrange the openings for securing the fixtures. Coaxially misaligned inlet and outlet fixtures will deform the sleeve, thus preventing accurate movement of the plunger and hence the stable operation of the pump.
When bending a plate to form the yoke the accuracy of bending should be high so as to precisely combine the yoke with the housing. It is also necessary to avoid the formation of any gap between the yoke and the component parts disposed between the opposing legs of the yoke.
When the openings are formed independently through respective legs it is difficult to maintain the openings in correct coaxial relation. To attempt to avoid this problem, these openings have been formed by advancing a drill from one side through both legs of a U shaped yoke. This method can improved the coaxial relationship but since both legs are separated, one of the legs is typically bent inwardly by the drill, thus impairing the coaxial arrangement.
When a U shaped yoke is used as above described, a high working accuracy is required for various component elements thus complicating the working and assembling operations with the result that the cost of manufacturing is increased.
Further, in the prior art electromagnetic pump, a bobbin for winding an exciting coil is fitted about the sleeve between the opposing legs of the yoke, and a printed substrate supporting electronic elements which comprise an oscillator for supplying pulsating current to the exciting coil is mounted on the outer ends of the legs of the yoke. Thus, the plunger is reciprocated in the sleeve by an electromagnetic force produced by the exciting coil and a return spring so as to feed liquid from an inlet passage of the inlet fixture to an outlet passage of the outlet fixture.
In most of the electromagnetic pumps of this type, the housing is also formed by bending a magnetic plate made of iron or steel so that when the printed substrate mounted on the outer ends of the legs of the yoke comes in contact with the inner surface of the housing a short circuiting path is formed. Accordingly, it is necessary to positively secure the printed substrate to the yoke to prevent disengagement of the substrate from the yoke legs due to shocks and vibrations. For this purpose, it is necessary to precisely construct various component parts so as to assure a proper gap between the inner surface of the housing and the printed substrate or to apply an insulating paper to the printed substrate.